Recently, there exists a need for reduction in size of electronic parts and thus for reduction in thickness of the parts used therein such as heat dissipation sheets.
Heat-dissipating fillers used in these electronic parts often contain both coarse powder of several μm to dozens of μm and fine powder of submicron to several μm and the fine powder has an important role in reducing the interfacial thermal resistance.
The particle shape of the heat-dissipating filler, especially of fine-powder heat-dissipating filler, is desirably spherical and spherical alumina fine powders have been mainly used traditionally. There is no example of a spherical boron nitride fine powder being used as the heat-dissipating filler.
Boron nitride is generally prepared by reacting a boron source (such as boric acid or borax) with a nitrogen source (such as urea, melamine, or ammonia) at high temperature, and known are, for example, a “pine cone”-shaped boron nitride, i.e., aggregation of scaly primary particles from boric acid and melamine, (Patent Document 1) and a spherical boron nitride prepared by spray-drying method (Patent Document 2).
Meanwhile, there are reports of spherical boron nitride fine powders being prepared by gas-phase synthesis method (Patent Documents 3, 4, and 5).
In the case of scaly boron nitride, there is a report on improvement in filling property by surface treatment in Patent Document 6 and Patent Document 6 discloses a method for producing a modified boron nitride comprising a step of mechanochemically treating scaly boron nitride in the presence of water or an organic solvent.